Note: You must install OpenCPN into your Applications folder where it belongs. The installers of the plugins expect it to be there.
Also for MacOS Mojave see CF thread http://www.cruisersforum.com/forums/f134/open-cpn-kind-of-a-mess-on-mojave-228973.html
For MacOS Catalina there are some issues, but look at this CF post http://www.cruisersforum.com/forums/f134/oesenc-does-not-download-to-plugins-on-opencpn-228875.html#post3054084
Use of your iPad with RealVNC and OpenCPN